Clinical significance of stress-induced ST segment elevation in patients with previous anterior myocardial infarction. Analysis of lactate metabolism with atrial pacing.

Abstract

To clarify the mechanism of stress-induced ST segment elevation in patients with previous anterior myocardial infarction, we examined myocardial lactate metabolism during atrial pacing in 32 patients with previous anterior myocardial infarction (MI group) and 11 control subjects (control group). In the MI group, atrial pacing resulted in new or additional ST segment elevation in leads with Q waves in 15 patients (ST elevation group), ST segment depression in 7 (ST depression group), but induced no appreciable ST segment changes in the remaining 10 patients (ST unchanged group). In all patients, the ST segment changes were identical to the results of exercise stress testing which was carried out prior to the atrial pacing. Lactate extraction ratio increased moderately during the atrial pacing in the control group (p less than 0.01). Although marked reduction of the myocardial lactate extraction ratio was noted in the ST depression group (p less than 0.05), no significant change in the ratio was evoked in the ST elevation group or the ST unchanged group during atrial pacing. Left ventricular end-diastolic pressure (LVEDP) increased markedly in the ST depression group during atrial pacing, but the elevation was less evident in the other groups. The ST elevation group demonstrated the lowest left ventricular ejection fraction and the severest degree of left ventricular asynergy. Thus, the present study indicates that aggravated left ventricular asynergy in the infarcted area and associated left ventricular dysfunction, rather than peri-infarction zone ischemia is a possible mechanism of stress-induced ST segment elevation in leads with Q waves following previous anterior myocardial infarction.